Conventionally, it has been attempted to increase edge components of the tread surface by means of providing plural of sipes in the land portion of the tread surface so as to realize excellent driving performance on icy-snowy road.
The provision of more sipes in the tread surface may increase the edge components thereof, however on the other hand, it deteriorates the rigidity of the land portion of the tread. In this case, the land portion is leaned and deformed by being loaded when the vehicle is braking, driving, or turning, and it caused a problem that the contact area of the tire and road surface is reduced and then the grounding property is deteriorated.
Patent Document 1 discloses a pneumatic tire comprising sipes which extends in a zigzag manner, having a bend portion with plural of bent points, from the side of the tread surface to the radially inward, to suppress the deformation of the land portion caused by the leaning of the land portion and maintain the grounding property of the tread surface.
However, when it comes to applying the sipes described in the patent document 1 to the tire for all seasons, which may be used not only on icy-snowy road but also on dry road and having large frictional coefficient and input a large force to the tread surface, there are cases especially as getting input on dry road that the edge of sipes are get involved between the tread surface and end up to be lacked.
Patent Document 2, in contrast, proposes to provide sipes having a perpendicular portion which extends to the normal direction from the tread surface S of the land portion, and a bend portion, being formed radially inward of the perpendicular portion and extends toward the bottom of the land portion while bending in the longitudinal direction of the tangent to the tread surface S. According to such configuration, it is possible, at the bend portion of the sipe, to suppress the deformation and leaning of the land portion, and at the perpendicular portion of the sipe, to prevent the lack of sipe edges.